Liking more than one person at a time and having sex with more than one person at a time are 2 completely different concepts.

The sooner you accept that, although the person you are committed to in return has committed themselves to you, they still have desires for anything 'beautiful' beyond yourself, the easier the relationship will be. The concept of love and marriage is not to blind yourself to the world for one person, but to love that one person and be with them, in spite of the beauty of the world. Once you get that carnal lust under control and devoted, it's fine to enjoy the company of others as well, so long as you aren't having sex with them.

It really depends on the situation. If you're just confused, then of course it's ok. The only problem with that is if you're in a semi-serious relationship (that could be considered cheating I guess?).

But yeah, I think it's just fine. So long as you're not confessing to both of them at the same time or anything lol.

I don't seem why it would ever be a problem to like more than one person. Even if you're in a relationship, I don't see why it would ever be a problem to just like someone. If you act on it without even mentioning it to your current partner, yeah that may be a problem, but just thinking about it really isn't that big of a deal.
Same goes for actually being with more than one person. As long as everyone in that relationship is accepting of it, it's not really an issue.